It is known that when, in a system in which the suction port of a suction device is open to the atmosphere, a gas is isotropically sucked from the suction port by depressurization of the interior of the system of the suction device through the use of a pressure reduction device, in a case where the pressure within the system of the suction device becomes lower than a certain pressure beyond a predetermined pressure, the speed of the gas passing through the suction port reaches a critical state, and thus the pressure at the suction port does not become lower than the certain pressure. The pressure of the suction port in the critical state is referred to as a critical pressure. Unless otherwise particularly specified, the pressure of the suction port is assumed to indicate a pressure in the center of the suction port. A critical pressure in an isentropic flow is determined by the specific heat ratio of a gas and the pressure of the atmosphere, and when atmospheric pressure is assumed to be 1013 hPa, the critical pressure in the atmosphere is 535 hPa.
In a conventional suction device in which suction is performed by bringing a suction target close to a suction port, since the pressure of the suction port is prevented from being equal to or less than a critical pressure, a suction force is limited. Furthermore, as another structural problem, when a gas is sucked from the suction port, a stagnation point where the flow speed is zero is generated on the surface of the suction target which is a suction point, and the pressure is increased to neat the atmospheric pressure at the stagnation point, with the result that the suction force becomes insufficient. Therefore, in a method of sucking the target surface of a target by sucking a gas from a suction port, which is a general suction method, it is impossible to obtain a high pressure reduction effect, and thus a suction force is limited.
On the other hand, the suction device which utilizes the suction method described above are industrially and widely used. Examples thereof include the suction of dust and dirt such as in a vacuum cleaner, the suction of fine particles and foreign substances adhering in the assembly processes of an electronic component and an electrical component, the suction of foreign substances in the manufacturing process of food and drink containers such as a PET bottle and the suction of chips and dust generated at the time of mechanical processing such as cutting or grinding. However, in the suction device, the suction force is limited due to the critical pressure and the stagnation point described above.
Therefore, in order to more enhance the suction effect, suction devices which use a vortex airflow are proposed in Patent Literatures 1 and 2. A vortex airflow is formed on the surface of a suction target, and thus it is possible to remove the stagnation point, which is one of the problems. A vortex airflow is formed by the rotation of an impeller wing in Patent Literature 1 and by jetting a gas to the inner circumferential surface of a suction nozzle in Patent Literature 2, and a pressure reduction effect in the center of the vertex is utilized, with the result that the suction effect is enhanced. However, although, in Patent Literature 1, it is necessary to accelerate the rotation of the impeller wing to the sound speed in order that the pressure of the suction port may become equal to or less than the critical pressure, it is structurally difficult to realize the acceleration. When as in Patent Literature 2, a vortex airflow is formed only by jetting of a gas, it is difficult to form such a high-speed swirl flow in which the pressure of the suction port is made equal to or less than the critical pressure.
Even in the field of laser processing, in drilling and cutting processing, along with irradiation with laser light, the generation of molten metal particles such as sputters, metal vapors referred to as fumes and fine metal particles referred to as debris is a problem in the case of a metal material, whereas in the case of a resin material, the generation of soot, smoke and a combustion gas is a problem in the case of a resin material. In laser decontamination, it is necessary to recover radioactive wastes scattered by the irradiation with laser. Note that, hereinafter, a scattered product generated from a laser irradiation portion by the irradiation with laser is referred to as a by-product. The by-product is a factor in lowering processing quality, and there is proposed a method of removing the by-product by using a suction device as described below.
Patent Literature 3 proposes a device in which a blow nozzle and a suction duct are disposed in the vicinity of a laser processing region, jetting and suction of a fluid are simultaneously performed and thus a by-product is prevented from adhering to a processing target.
Furthermore, Patent Literature 4 proposes a device in which a laser light irradiation surface is brought into a reduced-pressure atmosphere by provision of a local exhaust function, and reduction of processing energy and removal and recovery of the by-product are performed by irradiation with laser light.
However, the devices according to the two inventions described above are designed assuming that a flat plate such as a liquid crystal panel or a flat panel display is a processing target, and when being applied to a shaped product having large surface irregularities, in the device of Patent Literature 3, it is difficult to remove a by-product because a flow is blocked by the surface irregularities, whereas in the device of Patent Literature 4, it is necessary to keep short a distance between the bottom portion of a laser processing machine and the irradiation surface of the processing target, when step differences in the processing surface are large, the effect of sucking the by-product is lowered, and thus it is not possible to prevent the by-product from adhering again to a processing cross section.
Patent Literatures 5 and 6 propose a device which removes a by-product generated by laser processing by the action of a swirl flow (a spiral flow site and a vortex airflow). As the method of generating the swirl flow in the inventions, there is used a method of disposing a groove as a guide so as to form the swirl flow, and in this method, a force in a swirl direction is applied to the flow site by the effect of viscosity caused by a boundary layer in the vicinity of a groove wall surface to thereby form the swirl flow.
In order to more enhance the pressure reduction and suction effects produced by the swirl flow, it is necessary to increase the swirl speed of the swirl flow, but when the speed of the flow is increased, the thickness of the boundary layer in the vicinity of the wall surface is reduced and thus the effect of the viscosity is lowered and the flow site under the domination of inertia is formed, with the result that it becomes difficult to form the swirl flow. Accordingly, the pressure reduction and suction effects of the swirl flow formed by the device of Patent Literatures 5 and 6 are limited.